The present invention relates to the automated compilation of pieces of musical content, usually referred to as xe2x80x9ctracksxe2x80x9d, and more particularly, to compilation in which one track is phased in over the top of another, preferably in a manner providing an apparently seamless transition between tracks. This is known in current vernacular as xe2x80x9cmixingxe2x80x9d.
Our co-pending UK application (HP docket 30001926) discloses, inter alia, a system and method for the automated compilation of tracks which are typically stored as digital audio, such as on compact disc. In this system, the outputs of two digital audio players are fed to an output, such as a set of speakers. The speed at which tracks from the two CD players are played is adjusted, so that the beat of an incoming track is matched to the speed of a track currently playing (known as xe2x80x9ctime stretchingxe2x80x9d), and once this has been achieved an automated cross-fading device reduces the output volume of the current track while increasing the output volume of the incoming track, thereby to provide a seamless transition between them.
A first aspect of the present invention addresses the issue of amplification of each of the tracks during the transition phase from one track to another, or xe2x80x9ccross-fadexe2x80x9d. In an automated system, in order to try to provide a seamless transition between tracks, amplification of the outgoing track will typically be reduced at the same rate as the amplification of the incoming track is increased, with the reduction and increase in amplification starting at the same time. Frequently tracks are mixed so that the incoming track is faded in over the end of the outgoing track, as a result of which the volume on the outgoing track may well be reducing, since many dance tracks end simply by fading out the volume to zero, or start by fading in the volume from zero (i.e. the intrinsic amplitude or xe2x80x9cmastered volumexe2x80x9d of the recording is reduced to zero, or increased from zero, as the case may be). In such a situation, unless the fade-out rate of the intrinsic amplitude (and thus for a constant level of amplification, the volume) at the end of the outgoing track matches the fade-in rate of the intrinsic amplitude at the beginning of the incoming track, and both are in turn matched with the rate of cross-fading the amplification from one track to another, the transition between the tracks will be subject to a variation in volume which is undesirable, since it disturbs the seamless transition between incoming and outgoing tracks.
Accordingly, a first aspect of the present invention provides a method for the automated mixing of at least two pieces of musical content comprising the steps of:
selecting first and second sections of first and second tracks respectively, over which transition between playing the first and second tracks will be made;
sampling intrinsic recorded amplitude of the first and second tracks over the first and second sections respectively;
simultaneously playing the first and second sections of the first and second tracks;
effecting transition from playing the first track to playing the second track by reducing output volume of the first track over duration of the first section and increasing output volume of the second track over duration of the second section; and
using sampling of the intrinsic amplitude of at least one of the first and second tracks to equalise variations in net output volume from the first and second tracks over the duration of the transition.
Equalisation of variations in recorded amplitude may result merely in a reduction in variations of net output volume in comparison to what would otherwise be the case, or may result in a substantially constant net output volume, depending upon the extent of equalisation. Equalisation may be achieved typically either by altering the amplification of one or both tracks over the course of the transition, altering the intrinsic recorded amplitude of one or both tracks, or a combination of both techniques.
In one embodiment of equalisation by regulation of amplification for one or both of the tracks, a series of synchronous intrinsic amplitude values are sampled from each of the tracks, and contemporaneous values are then summed to determine the extent, if any, to which the combined intrinsic amplitude varies over the transition phase. The resultant variation in intrinsic amplitude is then used to generate an amplification profile which is then applied proportionally to one or both the tracks during the transition to equalise the net output volume. Equalisation by modification of intrinsic amplitude may use the contemporaneous summed amplitude values to generate discrete error values by which summed amplitude should be altered in order to maintain a constant value over the transition phase.
In an alternative embodiment amplification or intrinsic amplitude modification is used to configure predetermined sections of tracks to predetermined introduction and playout template profiles of amplitude against time, so that any two tracks conforming to the profile (either by variation in amplification or intrinsic amplitude) may be mixed together.
In yet a further embodiment an indication of variation in combined amplitude is generated for a plurality of temporal juxtapositions of two tracks, and the temporal juxtaposition having the lowest indicated variation is selected.
Typically, the equalisation will be performed on the basis of the sampling of the intrinsic amplitude in a particular frequency range determined as dominant, and this will in turn typically be determined on the basis of the frequency of the beat used for time stretching the incoming track and outgoing tracks.
A second and independent aspect of the present invention is concerned with the musical elements present in the outgoing and incoming tracks, such as vocal lines, melodic instrument parts, or percussion signatures (from, e.g. snare drums, symbols or handclaps etc.). It is not unusual for such elements in the outgoing and incoming tracks to clash, even though the fundamental beats of the two tracks have been matched, and the volume of the two tracks has been equalised over the cross fade. The result of such a clash is that when these elements are heard together the result is an unappealing mix.
Accordingly, a second aspect of the present invention provides a method for automated mixing of first and second music tracks comprising the steps of:
selecting first and second sections of the first and second tracks respectively, over which a transition between the first and second tracks will occur;
for at least selected intrinsic peak amplitudes of the first track, determining, in accordance with at least one predetermined criterion, whether a musical clash exists with an intrinsic peak amplitude from the second track; and
in the event of a clash, reducing output amplitude of at least one of the tracks at least at a frequency of one of the clashing intrinsic peak amplitudes, and over a time interval at least equal to duration of the aforesaid one of the intrinsic peak amplitudes.
The reduction in output amplitude (which will typically also be a reduction in output volume) of a given frequency band may again, as with the first aspect of the present invention, be implemented either via adjustment of amplification over at least the frequency of one of the clashing peak amplitudes (although this is only possible where the system provides for differing amplification levels for different frequency bands), or by copying at least the section of the track in question into addressable memory, and altering the intrinsic recorded amplitude levels for that frequency band.
Yet a further independent aspect of the present invention provides a method of mixing first and second tracks including the steps of:
analysing variations in amplitude with time and frequency for both tracks;
on the bas is of the analysis, defining at least one frequency band common to both tracks; and
equalising output amplitude of the tracks in the frequency band during mixing from one track to another.
Thus the frequency band to be used in order to provide equalisation is defined on the basis of the musical characteristics of the tracks to be mixed, rather than using predetermined frequency bands which may not be appropriate having regard to the frequencies of the two tracks to be mixed.